Spread spectrum multiple access (SSMA) techniques are attracting widespread attention in the personal communication fields, such as, for example, digital cellular radio. In SSMA systems, both the time and frequency domains may be shared by multiple users simultaneously. This simultaneous sharing of time and frequency domains is to be distinguished from time-division and frequency-division multiple access systems, TDMA and FDMA, where multiple user communication is facilitated with use of unique time slots or frequency bands, respectively, for each user.
In SSMA systems, such as direct-sequence code division multiple access (DS-CDMA) cellular systems, a base station may simultaneously transmit distinct information signals to separate users using a single band of frequencies. Individual information signals simultaneously transmitted in one frequency band may be identified and isolated by each receiving user because of the base station's utilization of a unique spreading sequence in the transmission of each information signal. Prior to transmission, the base station multiplies each information signal by a spreading sequence signal assigned to the user intended to receive the signal. This multiplication, performed by a "spreader," "spreads" the spectrum of the information signal over a "wide" frequency band shared by all users. To recover the correct signal from among those signals transmitted simultaneously in the wide frequency band, a receiving mobile user multiplies a received signal (containing all transmitted signals) by its own unique spreading sequence signal and integrates the result. These operations are performed by a "despreader." By so doing, the user "despreads" the received signals and identifies that signal intended for it, as distinct from other signals intended for other users.
The Telecommunications Institute of America ("TIA") recently adopted a SSMA standard that implements DS-CDMA technology. Telecommunications Institute of America, "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread-Spectrum Cellular System," 1993 (published as IS-95). This standard is called IS-95. However, we have recognized that spread spectrum systems, such as that described in the IS-95 standard, process certain signals inefficiently. This inefficient processing results in reduced system capacity and/or signal quality.